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RSS2016 Vol. 28, No. 01
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2016,
28: 010201.
doi: 10.11884/HPLPB201628.010201
Abstract:
Dragon-Ⅱaccelerator can provide three pulse electron beams under MHz repetition rate what the performance of each pulse electron beam is 18-20 MeV, 2.1 kA, 60 ns pulse length. Three pulses with adjustable spacing(300 ns minimum spacing) are delivered to the bremsstrahlung targets, generating three 1.7 mm(FWHM) spot size X-ray pulses with a dose of 7.7410-2C/kg (300 R) at 1 m. The key technology is analyzed in the accelerator development and the design requirements.
Dragon-Ⅱaccelerator can provide three pulse electron beams under MHz repetition rate what the performance of each pulse electron beam is 18-20 MeV, 2.1 kA, 60 ns pulse length. Three pulses with adjustable spacing(300 ns minimum spacing) are delivered to the bremsstrahlung targets, generating three 1.7 mm(FWHM) spot size X-ray pulses with a dose of 7.7410-2C/kg (300 R) at 1 m. The key technology is analyzed in the accelerator development and the design requirements.
2016,
28: 014001.
doi: 10.11884/HPLPB201628.014001
Abstract:
The measurement of repeatability for X-ray source position between several experiments was proposed. The difference between several images of the same object indicated the repeatability of the X-ray source position. First, a shell object was radiographed several times to get several images. And then the edge of each image was detected. By fitting the edge data of the image, the center position of the object in each experiment was obtained. The dataset of the center position showed the repeatability of the X-ray source position. The experiment results showed that the shift of the X-ray source position was less then 0.1 mm.
The measurement of repeatability for X-ray source position between several experiments was proposed. The difference between several images of the same object indicated the repeatability of the X-ray source position. First, a shell object was radiographed several times to get several images. And then the edge of each image was detected. By fitting the edge data of the image, the center position of the object in each experiment was obtained. The dataset of the center position showed the repeatability of the X-ray source position. The experiment results showed that the shift of the X-ray source position was less then 0.1 mm.
2016,
28: 014002.
doi: 10.11884/HPLPB201628.014002
Abstract:
High energy electron radiography(eRad) can quantitatively measure target material and its internal structure without taking target apart, it is a new NDT (nondestructive testing) technique. Compared with high energy proton radiography, eRad has submicron resolution and promises to be a powerful tool for mesoscale diagnosis. Its image blur is a crucial point that needs to be deeply studied. To study the influence of interaction and imaging beamline on image blur, numerical simulation using the Monte Carlo code Geant4 has been implemented, including the entire physics process of 12 GeV electron beam travelling through the object and beamline and arriving at the image plane. This article mainly analyzes the chromatic aberration of the imaging beamline, the blur of the longitudinal length of target and the influence of secondary particles using this model. The result shows that the scale of image blur in eRad is just submicron and most blur is caused by imaging beamline, the influence of longitudinal length of target and secondly particle can be neglected.
High energy electron radiography(eRad) can quantitatively measure target material and its internal structure without taking target apart, it is a new NDT (nondestructive testing) technique. Compared with high energy proton radiography, eRad has submicron resolution and promises to be a powerful tool for mesoscale diagnosis. Its image blur is a crucial point that needs to be deeply studied. To study the influence of interaction and imaging beamline on image blur, numerical simulation using the Monte Carlo code Geant4 has been implemented, including the entire physics process of 12 GeV electron beam travelling through the object and beamline and arriving at the image plane. This article mainly analyzes the chromatic aberration of the imaging beamline, the blur of the longitudinal length of target and the influence of secondary particles using this model. The result shows that the scale of image blur in eRad is just submicron and most blur is caused by imaging beamline, the influence of longitudinal length of target and secondly particle can be neglected.
2016,
28: 019901.
doi: 10.11884/HPLPB201628.019901
Abstract:
The SG-Ⅲ laser facility has successfully demonstrated its capability to deliver 60 TW/180 kJ ultraviolet laser (351 nm) onto the target, which establishes it the worlds second and Asias largest laser driver for inertial confinement fusion (ICF) research. On one hand, the construction of the SG-Ⅲ laser facility systematically advances and maturates a series of core capabilities of domestic high power laser field, such as integrated design, integrated installing, fine assembling and calibration, manufacture, optics diagnostics, key technologies, and so on. On the other hand, it represents that we have already developed an optical engineering system for future larger ICF laser driver research and construction.
The SG-Ⅲ laser facility has successfully demonstrated its capability to deliver 60 TW/180 kJ ultraviolet laser (351 nm) onto the target, which establishes it the worlds second and Asias largest laser driver for inertial confinement fusion (ICF) research. On one hand, the construction of the SG-Ⅲ laser facility systematically advances and maturates a series of core capabilities of domestic high power laser field, such as integrated design, integrated installing, fine assembling and calibration, manufacture, optics diagnostics, key technologies, and so on. On the other hand, it represents that we have already developed an optical engineering system for future larger ICF laser driver research and construction.
2016,
28: 014003.
doi: 10.11884/HPLPB201628.014003
Abstract:
This paper introduces a 450 kV digital X-ray diagnostic system composed of a 450 kV pulsed X-ray system and an anti-radiation X-ray CCD camera. The 450 kV pulsed X-ray system is designed according to the principle of bipolar charged Marx generator. The Marx generator is designed in coaxial structure, and low jitter field-distortion switches, isolation inductance and ceramic capacitors are used in the pulse generator to shorten pulse width of output pulse. The generator is connected with an X-ray tube through a high-voltage cable. For a charging voltage of 35 kV per stage, the Marx generator generates a more than 450 kV pulse voltage that is applied to the X-ray tube. The X-ray tube generates a dose of 5.210-6 C/kg at 1 m away for the flash X-radiography with pulse width of 40 ns. The size of X-ray source is 2-5 mm, the anti-radiation X-ray CCD camera receives the X-ray spectrum within the range of 10-450 keV, the effective imaging area is up to 100 mm100 mm, and the spatial resolution is up to 3 lp/mm. The experiment results show that the 450 kV digital X-ray diagnostic system has an imaging area no less than 70 mm, resolution greater than 1.2 lp/mm under the protection of 40 mm thick aluminium plate. It is the ideal tool for high-speed radiation photography.
This paper introduces a 450 kV digital X-ray diagnostic system composed of a 450 kV pulsed X-ray system and an anti-radiation X-ray CCD camera. The 450 kV pulsed X-ray system is designed according to the principle of bipolar charged Marx generator. The Marx generator is designed in coaxial structure, and low jitter field-distortion switches, isolation inductance and ceramic capacitors are used in the pulse generator to shorten pulse width of output pulse. The generator is connected with an X-ray tube through a high-voltage cable. For a charging voltage of 35 kV per stage, the Marx generator generates a more than 450 kV pulse voltage that is applied to the X-ray tube. The X-ray tube generates a dose of 5.210-6 C/kg at 1 m away for the flash X-radiography with pulse width of 40 ns. The size of X-ray source is 2-5 mm, the anti-radiation X-ray CCD camera receives the X-ray spectrum within the range of 10-450 keV, the effective imaging area is up to 100 mm100 mm, and the spatial resolution is up to 3 lp/mm. The experiment results show that the 450 kV digital X-ray diagnostic system has an imaging area no less than 70 mm, resolution greater than 1.2 lp/mm under the protection of 40 mm thick aluminium plate. It is the ideal tool for high-speed radiation photography.
2016,
28: 014004.
doi: 10.11884/HPLPB201628.014004
Abstract:
Monte Carlo imaging simulation is applied to investigate the impact of filter material properties on accurate and robust reconstruction of the high-energy X-ray spectrum based on the attenuated transmission principle. A model of multi-collimating apertures is designed to simulate the process of X-ray passing through filter materials, and an entire attenuation transmission curve is obtained in a single imaging simulation. It is an ill-conditioned problem to obtain the X-ray spectrum from the transmission data. An improved iterative perturbation method is used to reconstruct the spectrum, which considers minimization of the difference between the calculated and the true transmission curves and smoothness of the high-energy spectrum function. The inherent relation between the attenuation characteristic of the filter material and the accurate-and-robust reconstruction of the spectrum is also verified. The results show that the mass attenuation coefficient of the filter material should be monotonically decreasing over the spectrum.
Monte Carlo imaging simulation is applied to investigate the impact of filter material properties on accurate and robust reconstruction of the high-energy X-ray spectrum based on the attenuated transmission principle. A model of multi-collimating apertures is designed to simulate the process of X-ray passing through filter materials, and an entire attenuation transmission curve is obtained in a single imaging simulation. It is an ill-conditioned problem to obtain the X-ray spectrum from the transmission data. An improved iterative perturbation method is used to reconstruct the spectrum, which considers minimization of the difference between the calculated and the true transmission curves and smoothness of the high-energy spectrum function. The inherent relation between the attenuation characteristic of the filter material and the accurate-and-robust reconstruction of the spectrum is also verified. The results show that the mass attenuation coefficient of the filter material should be monotonically decreasing over the spectrum.
2016,
28: 014005.
doi: 10.11884/HPLPB201628.014005
Abstract:
A low impedance large surface diode system with high purity graphite ring cathode and organic glass insulation is developed. The diode is optimally designed by using theoretical calculation and numerical simulation. Under the premise of ensuring the insulation safety, the axial length and the gap between the inner and outer canisters of diode are cut down to decrease the inductance of diode. The experimental result shows that the diode after optimal design works stably without breakdown at the voltage of 200 kV. The result with a max voltage of 213 kV, a current of 221 kA, a characteristic impedance of 1 , a current density of 8 kA/cm2 and an FWHM of 50 ns is achieved in the experiment.
A low impedance large surface diode system with high purity graphite ring cathode and organic glass insulation is developed. The diode is optimally designed by using theoretical calculation and numerical simulation. Under the premise of ensuring the insulation safety, the axial length and the gap between the inner and outer canisters of diode are cut down to decrease the inductance of diode. The experimental result shows that the diode after optimal design works stably without breakdown at the voltage of 200 kV. The result with a max voltage of 213 kV, a current of 221 kA, a characteristic impedance of 1 , a current density of 8 kA/cm2 and an FWHM of 50 ns is achieved in the experiment.
2016,
28: 014006.
doi: 10.11884/HPLPB201628.014006
Abstract:
It was hard to measure the fluence of pulse hard X-ray directly in the field of high power particle beam. The method of measuring the fluence of pulse hard X-ray was defined, and the basic theory of full-cell processes was introduced. The phototubes and LSO scintillators were used to develop the measurement system. The influence of all measurement units was analysed. By using the MCNP Monte-Carlo code, the energy deposition and transmissivity in axial region of the LSO scintillators were calculated when the photons of different energies irradiated the scintillators of different thicknesses. The thickness of the LSO scintillator was given, which was 20 mm. The collimation system and anti-electromagnetic interference system were designed. The signal-to-noise ratio was added.
It was hard to measure the fluence of pulse hard X-ray directly in the field of high power particle beam. The method of measuring the fluence of pulse hard X-ray was defined, and the basic theory of full-cell processes was introduced. The phototubes and LSO scintillators were used to develop the measurement system. The influence of all measurement units was analysed. By using the MCNP Monte-Carlo code, the energy deposition and transmissivity in axial region of the LSO scintillators were calculated when the photons of different energies irradiated the scintillators of different thicknesses. The thickness of the LSO scintillator was given, which was 20 mm. The collimation system and anti-electromagnetic interference system were designed. The signal-to-noise ratio was added.
2016,
28: 015001.
doi: 10.11884/HPLPB201628.015001
Abstract:
Avalanche transistor is a kind of ideal semiconductor device which can provide fast response and high pulse power at the same time, it can conveniently produce high power pulse with nano/subnanosecond rising edge. In this paper, three different types of circuits based on avalanche transistors are made. The performances of these circuits with different stages are compared. Besides, the effect of cable length on the pulse output is studied. The experiment results show that the pulse rising edge of circuit with cable as energy storage component can be divided into a fast rising stage (0.4 ns) followed by a much slower stage, while the output of circuit with capacitor as energy storage component only has the 0.4 ns fast rising stage, which indicate that the wave propagation in the cable affect the occurrence of an avalanche, therefore affecting the circuit output performance.
Avalanche transistor is a kind of ideal semiconductor device which can provide fast response and high pulse power at the same time, it can conveniently produce high power pulse with nano/subnanosecond rising edge. In this paper, three different types of circuits based on avalanche transistors are made. The performances of these circuits with different stages are compared. Besides, the effect of cable length on the pulse output is studied. The experiment results show that the pulse rising edge of circuit with cable as energy storage component can be divided into a fast rising stage (0.4 ns) followed by a much slower stage, while the output of circuit with capacitor as energy storage component only has the 0.4 ns fast rising stage, which indicate that the wave propagation in the cable affect the occurrence of an avalanche, therefore affecting the circuit output performance.
2016,
28: 015002.
doi: 10.11884/HPLPB201628.015002
Abstract:
A triple resonance pulse transformer is developed based on a taper dual-winding magnetic core transformer, it has the advantages of is compact structure, small size and so on. The magnetic core of the transformer is made of 0.08 mm thick silicon steel strip with semilunar structure, and fastened in an aluminum cylinder. The primary and secondary windings consist of double parallel coils. Two taper high voltage windings are symmetrically wound in the groove of the organic glass skeleton and two output ends are welded together and drawn from axis of the cylinder. This structure may improve electric field distribution of the high voltage winding and achieve a coaxial output. The triple resonance circuit is composed of the core transformer, LC tuning circuit and a pulse forming line (27 pF). The tuning capacitor is the structure capacitance of a short coaxial transmission line, and the tuning inductor is wound in the non-uniform grooves of the organic glass skeleton with 0.08 mm diameter enameled wire. The experimental results indicate that the peak output voltage of the triple resonance pulse transformer is about 800 kV and the charging time is about 650 ns.It is demonstrated that a triple resonance pulse transformer can be developed based on a magnetic core pulse transformer.
A triple resonance pulse transformer is developed based on a taper dual-winding magnetic core transformer, it has the advantages of is compact structure, small size and so on. The magnetic core of the transformer is made of 0.08 mm thick silicon steel strip with semilunar structure, and fastened in an aluminum cylinder. The primary and secondary windings consist of double parallel coils. Two taper high voltage windings are symmetrically wound in the groove of the organic glass skeleton and two output ends are welded together and drawn from axis of the cylinder. This structure may improve electric field distribution of the high voltage winding and achieve a coaxial output. The triple resonance circuit is composed of the core transformer, LC tuning circuit and a pulse forming line (27 pF). The tuning capacitor is the structure capacitance of a short coaxial transmission line, and the tuning inductor is wound in the non-uniform grooves of the organic glass skeleton with 0.08 mm diameter enameled wire. The experimental results indicate that the peak output voltage of the triple resonance pulse transformer is about 800 kV and the charging time is about 650 ns.It is demonstrated that a triple resonance pulse transformer can be developed based on a magnetic core pulse transformer.
2016,
28: 015003.
doi: 10.11884/HPLPB201628.015003
Abstract:
The paper introduces a compact 200 kV/200 kA pulse source for hard X ray driving source. It consists of power storage Marx generator, water medium forming line and transmission line, gas switch, and load. It was optimized to include changing resistance water medium line, high pressure gas switch and peaking switch. When the Marx generator is charged with 60 kV voltage, the output of the match load can generate a pulse with 200 kV/200 kA, rise time 40 ns, width 40 ns. The pulse source will be used for the study of 1 diode, pressure gas switch, synchronized trigger and the diagnosis for plasma emitting.
The paper introduces a compact 200 kV/200 kA pulse source for hard X ray driving source. It consists of power storage Marx generator, water medium forming line and transmission line, gas switch, and load. It was optimized to include changing resistance water medium line, high pressure gas switch and peaking switch. When the Marx generator is charged with 60 kV voltage, the output of the match load can generate a pulse with 200 kV/200 kA, rise time 40 ns, width 40 ns. The pulse source will be used for the study of 1 diode, pressure gas switch, synchronized trigger and the diagnosis for plasma emitting.
2016,
28: 015004.
doi: 10.11884/HPLPB201628.015004
Abstract:
In order to satisfy the requirement of the lower hybrid current driven(LHCD) system on HL-2A, the high voltage power supply based on pulse step modulator is designed and analyzed. Many modules are connected in series, and the output voltage can be adjusted continuously. The power supply with low voltage and low frequency can be transferred into the power supply with high voltage and high frequency. The power and stability and redundancy are increased. The parameter and type of the components in the module including their technology layout are analyzed carefully. The leakage inductance of the multi-winding transformer is used as the filter inductor. The metallized film capacitors and the IGBT are adopted. The high voltage transformers with 29 second-windings are designed. The control algorithm and control system are designed to satisfy the requirement of the load. Test results especially the over-current protective test results are shown. The practicabilities of the two main control algorithms are tested. Many parameters especially those for quick protection and stability of the power supply can satisfy the requirement of the load.
In order to satisfy the requirement of the lower hybrid current driven(LHCD) system on HL-2A, the high voltage power supply based on pulse step modulator is designed and analyzed. Many modules are connected in series, and the output voltage can be adjusted continuously. The power supply with low voltage and low frequency can be transferred into the power supply with high voltage and high frequency. The power and stability and redundancy are increased. The parameter and type of the components in the module including their technology layout are analyzed carefully. The leakage inductance of the multi-winding transformer is used as the filter inductor. The metallized film capacitors and the IGBT are adopted. The high voltage transformers with 29 second-windings are designed. The control algorithm and control system are designed to satisfy the requirement of the load. Test results especially the over-current protective test results are shown. The practicabilities of the two main control algorithms are tested. Many parameters especially those for quick protection and stability of the power supply can satisfy the requirement of the load.
2016,
28: 015005.
doi: 10.11884/HPLPB201628.015005
Abstract:
A 0.1 Hz, 800 kA LTD stage for the Z-pinch driven fusion-fission hybrid reactor (Z-FFR) has been developed. The stage consists of 34 bricks, which are coupled through 4 matglas magnetic cores. Each brick has two 40 nF/100 kV capacitors and a gas switch of 4 gaps in series, and the loop inductance is 272 nH. The LTD stage can deliver about 800 kA current pulse with a rise time of 100 ns into the matched liquid resistive load with a repetitive frequency of 0.1 Hz. A novel trigger way that only one trigger cable triggers the stage via a continuous trigger bus internal to the stage has been proposed and demonstrated. The experimental results show that the new trigger way is feasible and reliable. A 140 kV, 25 ns rising time trigger pulse and a 5.2 kA, 30 s width pre-magnetization current pulse which can operate with a rep-rate of 0.1 Hz were used in this stage to insure the LTD stage generate a 80 kV/800 kA current pulse every 10 s. A multi-stage gas switch that has a lifetime in excess of 10000 shots and a jitter of less than 3 ns one sigma agrees well with the demand of Z-FFR.
A 0.1 Hz, 800 kA LTD stage for the Z-pinch driven fusion-fission hybrid reactor (Z-FFR) has been developed. The stage consists of 34 bricks, which are coupled through 4 matglas magnetic cores. Each brick has two 40 nF/100 kV capacitors and a gas switch of 4 gaps in series, and the loop inductance is 272 nH. The LTD stage can deliver about 800 kA current pulse with a rise time of 100 ns into the matched liquid resistive load with a repetitive frequency of 0.1 Hz. A novel trigger way that only one trigger cable triggers the stage via a continuous trigger bus internal to the stage has been proposed and demonstrated. The experimental results show that the new trigger way is feasible and reliable. A 140 kV, 25 ns rising time trigger pulse and a 5.2 kA, 30 s width pre-magnetization current pulse which can operate with a rep-rate of 0.1 Hz were used in this stage to insure the LTD stage generate a 80 kV/800 kA current pulse every 10 s. A multi-stage gas switch that has a lifetime in excess of 10000 shots and a jitter of less than 3 ns one sigma agrees well with the demand of Z-FFR.
2016,
28: 015006.
doi: 10.11884/HPLPB201628.015006
Abstract:
Due to the coupling problem, the output efficiency of the accelerating unit for the dielectric wall accelerator is reduced. With electromagnetic field simulation software based on FDTD method, the multi-plate Blumlein lines loading the high gradient insulator(HGI) is analyzed. The simulation includes one and three groups of 1-stage and 15-stage Blumlein line(BL) respectively loading HGIs. The results show more parallel electrodes in multi-BLs bring itself a large coupling capacitance, which leads to a slower rising edge and a lower amplitude. The output efficiency drops when three groups of multi-BLs work together because the adjacent group of multi-stage-BLs become a coupling capacitor and split current seriously. At the same time, the adjacent group of multi-stage BLs also discharge and affect output efficiency. A preliminary optimization is studied. By rotating every BL stages a certain angle to reduce the effective opposite area of parallel electrodes, the group of multi-BLs decreases its own coupling capacitance, and some benefit achieved. However, it requires further verification whether the optimization can reduce the coupling capacitance between the BL modules.
Due to the coupling problem, the output efficiency of the accelerating unit for the dielectric wall accelerator is reduced. With electromagnetic field simulation software based on FDTD method, the multi-plate Blumlein lines loading the high gradient insulator(HGI) is analyzed. The simulation includes one and three groups of 1-stage and 15-stage Blumlein line(BL) respectively loading HGIs. The results show more parallel electrodes in multi-BLs bring itself a large coupling capacitance, which leads to a slower rising edge and a lower amplitude. The output efficiency drops when three groups of multi-BLs work together because the adjacent group of multi-stage-BLs become a coupling capacitor and split current seriously. At the same time, the adjacent group of multi-stage BLs also discharge and affect output efficiency. A preliminary optimization is studied. By rotating every BL stages a certain angle to reduce the effective opposite area of parallel electrodes, the group of multi-BLs decreases its own coupling capacitance, and some benefit achieved. However, it requires further verification whether the optimization can reduce the coupling capacitance between the BL modules.
2016,
28: 015007.
doi: 10.11884/HPLPB201628.015007
Abstract:
In order to conduct experimental study effectively, the scaling method used in a small or medium caliber railgun launcher was analyzed and improved. In consideration of the feasibility of the experimental conditions, studies on the electromagnetic field and loading capacity were conducted under the condition that the material properties were constant. In addition, related simulations were carried out to prove the scaling model. Results indicate that there are various scaling methods. In a large diameter rail launcher with relatively low conductivity, the physical fields can match the model launcher which has higher conductivity.
In order to conduct experimental study effectively, the scaling method used in a small or medium caliber railgun launcher was analyzed and improved. In consideration of the feasibility of the experimental conditions, studies on the electromagnetic field and loading capacity were conducted under the condition that the material properties were constant. In addition, related simulations were carried out to prove the scaling model. Results indicate that there are various scaling methods. In a large diameter rail launcher with relatively low conductivity, the physical fields can match the model launcher which has higher conductivity.
2016,
28: 015008.
doi: 10.11884/HPLPB201628.015008
Abstract:
High-voltage pulse fracturing technology is based on the electro-hydraulic effect principle, where strong shock wave generated by the discharge of water pulse creates cracks in the rock. It has become a hot research subject in the field of rock fracturing. This paper sets up two types of current source modules applied to the water discharge, the single and the double current source modules. And the electrodes voltage and current waveforms of the modules are explored by the needle electrodes at different discharge voltage with 1mm electrode gap. The experimental results show that at the same discharge voltage without any load, the double module generates greater discharge current, resulting in higher instantaneous power at the time of discharge; while for underwater discharge, there is a great randomness in the pre-breakdown time of the water gaps. The minimum and maximum standard deviations of the pre-breakdown time for the single module are 0. 285 ms and 1. 481 ms respectively, while for the double module, the minimum and maximum deviations are 0. 369 ms and 0. 703 ms. From the overall trend, the higher the discharge voltage is, the shorter the pre-breakdown time will be: the average time of the double module varies from 2. 686 ms at 1300 V to 1. 036 ms at 1800 V.
High-voltage pulse fracturing technology is based on the electro-hydraulic effect principle, where strong shock wave generated by the discharge of water pulse creates cracks in the rock. It has become a hot research subject in the field of rock fracturing. This paper sets up two types of current source modules applied to the water discharge, the single and the double current source modules. And the electrodes voltage and current waveforms of the modules are explored by the needle electrodes at different discharge voltage with 1mm electrode gap. The experimental results show that at the same discharge voltage without any load, the double module generates greater discharge current, resulting in higher instantaneous power at the time of discharge; while for underwater discharge, there is a great randomness in the pre-breakdown time of the water gaps. The minimum and maximum standard deviations of the pre-breakdown time for the single module are 0. 285 ms and 1. 481 ms respectively, while for the double module, the minimum and maximum deviations are 0. 369 ms and 0. 703 ms. From the overall trend, the higher the discharge voltage is, the shorter the pre-breakdown time will be: the average time of the double module varies from 2. 686 ms at 1300 V to 1. 036 ms at 1800 V.
2016,
28: 015009.
doi: 10.11884/HPLPB201628.015009
Abstract:
In this paper, DPHCs function in PTS facility was preliminarily explored using NEPTUNE3D code. A series of cold-chamber tests were calculated and analyzed, in which only the electron emission on cathode surface was considered without energy deposition and temperature rise. In order to calculate the acceleration, a simplified 3D geometry model was developed and used as an initial parameter. The full-circuit way about PTS facility was simulated in order to acquire voltage curves from vacuum insulator B under different loads, which were used as input driving signals in following PIC simulations. With the help of visualization tools, the distribution of the magnetic field and the clearer positions of magnetic nulls were both acquired and displayed in 2D and 3D schematics. Calculated results and data proved that DPHC behaved efficiently during current transforming and energy convergence. Preliminary research about the process of electron emission and transportation under high voltage curve were explored, and the current loss efficiencies were estimated to be around 0.46%~0.48% under different driving sources. The simulation results let us understand the DPHC functions in pulsed power systems better.
In this paper, DPHCs function in PTS facility was preliminarily explored using NEPTUNE3D code. A series of cold-chamber tests were calculated and analyzed, in which only the electron emission on cathode surface was considered without energy deposition and temperature rise. In order to calculate the acceleration, a simplified 3D geometry model was developed and used as an initial parameter. The full-circuit way about PTS facility was simulated in order to acquire voltage curves from vacuum insulator B under different loads, which were used as input driving signals in following PIC simulations. With the help of visualization tools, the distribution of the magnetic field and the clearer positions of magnetic nulls were both acquired and displayed in 2D and 3D schematics. Calculated results and data proved that DPHC behaved efficiently during current transforming and energy convergence. Preliminary research about the process of electron emission and transportation under high voltage curve were explored, and the current loss efficiencies were estimated to be around 0.46%~0.48% under different driving sources. The simulation results let us understand the DPHC functions in pulsed power systems better.
2016,
28: 015010.
doi: 10.11884/HPLPB201628.015010
Abstract:
Parasite parameters caused by winding have negative impact on broadband complex permeability measurement. This paper identifies the effects of winding resistance, parasite capacitor and leakage inductance. The impact of each parasite parameter is quantitatively determined and an improved measurement method is proposed to mitigate the influence of the parasite parameters. Furthermore, commonly used complex permeability models are introduced. The Levy method and iterative rational function approaching (IRFA) method are used to extract model parameters. The proposed method has been applied to three different kinds of magnetic materials and satisfactory results have been obtained, which conforms the proposed measurement method and parameter extraction algorithms are suitable for building the small-signal model for magnetic materials.
Parasite parameters caused by winding have negative impact on broadband complex permeability measurement. This paper identifies the effects of winding resistance, parasite capacitor and leakage inductance. The impact of each parasite parameter is quantitatively determined and an improved measurement method is proposed to mitigate the influence of the parasite parameters. Furthermore, commonly used complex permeability models are introduced. The Levy method and iterative rational function approaching (IRFA) method are used to extract model parameters. The proposed method has been applied to three different kinds of magnetic materials and satisfactory results have been obtained, which conforms the proposed measurement method and parameter extraction algorithms are suitable for building the small-signal model for magnetic materials.
2016,
28: 015011.
doi: 10.11884/HPLPB201628.015011
Abstract:
The surface damage of the lens in high voltage, high current laser triggered gas switch is analyzed, based on the measurements of optical transmission, the analysis of the mist material on the lens surface and the statistic of exposure time. Both the corrosion and the debris/dust deposition on the lens surface have some effect on the optical transmission, which leads to the failure. From the comparison of three different structure laser triggered switches and the statistics of their operation data, it is concluded that both HF and debris/dust can be greatly eliminated by using the CaF2 lens, low water imbibitions insulation materials, and tungsten-copper electrode. The operation time of the switch can be prolonged with dehydration processing of the components. The axial insulated V/N type assistant multilevel gap switch has the longest operation life.
The surface damage of the lens in high voltage, high current laser triggered gas switch is analyzed, based on the measurements of optical transmission, the analysis of the mist material on the lens surface and the statistic of exposure time. Both the corrosion and the debris/dust deposition on the lens surface have some effect on the optical transmission, which leads to the failure. From the comparison of three different structure laser triggered switches and the statistics of their operation data, it is concluded that both HF and debris/dust can be greatly eliminated by using the CaF2 lens, low water imbibitions insulation materials, and tungsten-copper electrode. The operation time of the switch can be prolonged with dehydration processing of the components. The axial insulated V/N type assistant multilevel gap switch has the longest operation life.
2016,
28: 015012.
doi: 10.11884/HPLPB201628.015012
Abstract:
An improved coaxial high-voltage ceramic vacuum interface applied in a repetitive pulse generator, was designed and tested. Results from electro-static calculation by ANSYS show that the electric field (E-field) distribution within the improved interface is uniform. Key structures such as the anode and the cathode shielding rings of the ceramic insulator were optimized to significantly reduce E-field stresses. Aging experiments with this interface were conducted in the condition of about 600 kV, 80 ns and 1-5 Hz pulses. The preliminary test shows that the ceramic vacuum interface can work stably with the hold-off field of more than 44 kV/cm. The experimental results agree with the simulated results. Finally, the influence of the surface treatment on the ceramic flashover characteristics was discussed.
An improved coaxial high-voltage ceramic vacuum interface applied in a repetitive pulse generator, was designed and tested. Results from electro-static calculation by ANSYS show that the electric field (E-field) distribution within the improved interface is uniform. Key structures such as the anode and the cathode shielding rings of the ceramic insulator were optimized to significantly reduce E-field stresses. Aging experiments with this interface were conducted in the condition of about 600 kV, 80 ns and 1-5 Hz pulses. The preliminary test shows that the ceramic vacuum interface can work stably with the hold-off field of more than 44 kV/cm. The experimental results agree with the simulated results. Finally, the influence of the surface treatment on the ceramic flashover characteristics was discussed.
2016,
28: 015013.
doi: 10.11884/HPLPB201628.015013
Abstract:
A compact repetitive PFN-Marx generator was constructed for the application of generating electron beams. The generator has twenty-two stages with inductive isolation. Each stage consists of twenty-one ceramic capacitors which may be charged the maximal voltage of 60 kV by a pulse transformer in 50 s. A compact Marx trigger with the integrated design of a pulse transformer and a magnetic switch which have a common magnetic core was also fabricated. The generator can operate at 5 Hz rep-rate with the output power of 7 GW, the impedance of 40 and the pulse width of 100 ns. Changing the capacitor units, an improved generator with the impedance of 50 and the pulse width of 70 ns generates ten pulses of one burst with the power of 8 GW at 10 Hz rep-rate. An S-band magnetron driven by the improved generator has generated microwave output with the power of 1 GW at the frequency of 2.32 GHz, which preliminarily shows the generators ability of driving high power microwave devices.
A compact repetitive PFN-Marx generator was constructed for the application of generating electron beams. The generator has twenty-two stages with inductive isolation. Each stage consists of twenty-one ceramic capacitors which may be charged the maximal voltage of 60 kV by a pulse transformer in 50 s. A compact Marx trigger with the integrated design of a pulse transformer and a magnetic switch which have a common magnetic core was also fabricated. The generator can operate at 5 Hz rep-rate with the output power of 7 GW, the impedance of 40 and the pulse width of 100 ns. Changing the capacitor units, an improved generator with the impedance of 50 and the pulse width of 70 ns generates ten pulses of one burst with the power of 8 GW at 10 Hz rep-rate. An S-band magnetron driven by the improved generator has generated microwave output with the power of 1 GW at the frequency of 2.32 GHz, which preliminarily shows the generators ability of driving high power microwave devices.
2016,
28: 015014.
doi: 10.11884/HPLPB201628.015014
Abstract:
In order to study the electromagnetic pulse forming and transmission in the PTS facility, and to optimize the performance to get the desired driving currents for the load design, a full circuit model were founded to describe the charging and discharging process for all the key circuit elements in detail. The model and parameters were validated and the numerical results coincided with the experimental results. For typical Z pinch loads, the compression of the pulse and the amplification of the pulse power were simulated, as charged at a voltage of 65 kV, the PTS facility delivered about 1 MJ energy to the stack region. For typical isentropic compression experiments, the timing of the laser triggered gas switch was designed for different loads, and the tailored currents with about 6 MA in peak and 450 ns(0-100%) in rise time were obtained in the load region from simulation for shot 0121.
In order to study the electromagnetic pulse forming and transmission in the PTS facility, and to optimize the performance to get the desired driving currents for the load design, a full circuit model were founded to describe the charging and discharging process for all the key circuit elements in detail. The model and parameters were validated and the numerical results coincided with the experimental results. For typical Z pinch loads, the compression of the pulse and the amplification of the pulse power were simulated, as charged at a voltage of 65 kV, the PTS facility delivered about 1 MJ energy to the stack region. For typical isentropic compression experiments, the timing of the laser triggered gas switch was designed for different loads, and the tailored currents with about 6 MA in peak and 450 ns(0-100%) in rise time were obtained in the load region from simulation for shot 0121.
2016,
28: 015015.
doi: 10.11884/HPLPB201628.015015
Abstract:
Isentropic compression experiments have been developed for the study of the equation of state for materials at extreme pressures. We use the PTS facility to achieve a quasi-isentropic compression and hyper-velocity flyer launch. A series of experiments for the understanding of the load configuration design, such as the load structure, the electrode gap and plate size, are presented, analyzed, and compared. The electromagnetic simulation has been used to analyze the magnetic fields amplitude and uniformity on the inner surfaces of the load configurations. Some load configurations are designed for the study of the uniformity and consistency of the magnetic pressures on the electrode surfaces by a ramped compression wave. Based on the simulation and experiments, a stripline load configuration is chosen to enhance the magnetic pressures and improve the PTSs performance for isentropic compression experiments. Until now, an isentropic pressure of about 100 GPa and more than 10 km/s flyer launch demonstrated on the PTS facility have been obtained using the stripline loads.
Isentropic compression experiments have been developed for the study of the equation of state for materials at extreme pressures. We use the PTS facility to achieve a quasi-isentropic compression and hyper-velocity flyer launch. A series of experiments for the understanding of the load configuration design, such as the load structure, the electrode gap and plate size, are presented, analyzed, and compared. The electromagnetic simulation has been used to analyze the magnetic fields amplitude and uniformity on the inner surfaces of the load configurations. Some load configurations are designed for the study of the uniformity and consistency of the magnetic pressures on the electrode surfaces by a ramped compression wave. Based on the simulation and experiments, a stripline load configuration is chosen to enhance the magnetic pressures and improve the PTSs performance for isentropic compression experiments. Until now, an isentropic pressure of about 100 GPa and more than 10 km/s flyer launch demonstrated on the PTS facility have been obtained using the stripline loads.
2016,
28: 015016.
doi: 10.11884/HPLPB201628.015016
Abstract:
The high-voltage DC power supply is widely used in scientific experiments and industrial production. To meet the requirements of high stability and low ripple of high voltage power for EBIT, the paper focuses on a designing a high-voltage DC power supply. The main circuits make use of the high frequency inversion circuit, duple voltage rectifying circuit and voltage and current dual-loop control to get the high DC voltage. The experimental results show that the DC high voltage power has good stability, small ripple, high reliability, system security, and it meets the test requirements.
The high-voltage DC power supply is widely used in scientific experiments and industrial production. To meet the requirements of high stability and low ripple of high voltage power for EBIT, the paper focuses on a designing a high-voltage DC power supply. The main circuits make use of the high frequency inversion circuit, duple voltage rectifying circuit and voltage and current dual-loop control to get the high DC voltage. The experimental results show that the DC high voltage power has good stability, small ripple, high reliability, system security, and it meets the test requirements.
2016,
28: 015017.
doi: 10.11884/HPLPB201628.015017
Abstract:
As the glycerol medium has important applications in the pulse forming line, its breakdown characteristics are studied experimentally in a scaled coaxial specimen under different conditions, including electrode surface, magnetic field, bubbles and so on. A thyristor controlled air-core pulse transformer with a maximum output voltage of 500 kV and the rising time of 26 s is built. A coaxial breakdown specimen immersed in pulsed magnetic field with the maximum magnetic field of 1 T is designed. Through the control of thyristors, the breakdown can be limited in the quasi stationary magnetic field. Four coaxial electrodes with the same shape but different surface disposed measures including sanding, wool polishing, metal electroplating and nonmetal electroplating are manufactured. The experimental results show that the breakdown of the glycerol has no polarity; the magnetic field of 1 T has no effect on the breakdown characteristics of the glycerin; different electrodes have significantly different microcosmic morphologies, resulting in the differences between breakdown characteristics of the glycerol, indicating that some kind of electronical process on the electrode surface has much influence on the breakdown; the probability of breakdown in glycerol can be reduced by evacuating the bubbles with large diameters, and the generated tiny bubbles after the breakdown reduce the average breakdown strength of the glycerol.
As the glycerol medium has important applications in the pulse forming line, its breakdown characteristics are studied experimentally in a scaled coaxial specimen under different conditions, including electrode surface, magnetic field, bubbles and so on. A thyristor controlled air-core pulse transformer with a maximum output voltage of 500 kV and the rising time of 26 s is built. A coaxial breakdown specimen immersed in pulsed magnetic field with the maximum magnetic field of 1 T is designed. Through the control of thyristors, the breakdown can be limited in the quasi stationary magnetic field. Four coaxial electrodes with the same shape but different surface disposed measures including sanding, wool polishing, metal electroplating and nonmetal electroplating are manufactured. The experimental results show that the breakdown of the glycerol has no polarity; the magnetic field of 1 T has no effect on the breakdown characteristics of the glycerin; different electrodes have significantly different microcosmic morphologies, resulting in the differences between breakdown characteristics of the glycerol, indicating that some kind of electronical process on the electrode surface has much influence on the breakdown; the probability of breakdown in glycerol can be reduced by evacuating the bubbles with large diameters, and the generated tiny bubbles after the breakdown reduce the average breakdown strength of the glycerol.
2016,
28: 015018.
doi: 10.11884/HPLPB201628.015018
Abstract:
The design scheme of a trigger generator applied to multiple spark gaps based on Tesla pulse transformer was proposed. The voltage distribution characteristics of multiple spark gaps under DC and pulse voltage were introduced, and the main influence factors of the voltage distribution under pulse voltage were given. By using a simulation software, the influences of the trigger frequency, dividing capacitor and equalizing resistor on the voltage distribution were analyzed and the optimal parameter setting of the trigger network was obtained. Take 10 spark gaps for example, the key parameters of Tesla transformer were determined based on the three elements of pulse steepness, output amplitude and loading capacity. When the coupling coefficient of Tesla pulse transformer was 0.7, the primary inductance was 2500 nH, the secondary inductance was 400 mH，the primary capacitor was 60 F and the charging voltage of the primary capacitance was 2.0 kV, the trigger voltage could achieve a trigger of ten-series spark gap. Combined with the multiple spark gap experiment, the work process of the Tesla pulse transformer applied to multiple spark gaps was investigated.
The design scheme of a trigger generator applied to multiple spark gaps based on Tesla pulse transformer was proposed. The voltage distribution characteristics of multiple spark gaps under DC and pulse voltage were introduced, and the main influence factors of the voltage distribution under pulse voltage were given. By using a simulation software, the influences of the trigger frequency, dividing capacitor and equalizing resistor on the voltage distribution were analyzed and the optimal parameter setting of the trigger network was obtained. Take 10 spark gaps for example, the key parameters of Tesla transformer were determined based on the three elements of pulse steepness, output amplitude and loading capacity. When the coupling coefficient of Tesla pulse transformer was 0.7, the primary inductance was 2500 nH, the secondary inductance was 400 mH，the primary capacitor was 60 F and the charging voltage of the primary capacitance was 2.0 kV, the trigger voltage could achieve a trigger of ten-series spark gap. Combined with the multiple spark gap experiment, the work process of the Tesla pulse transformer applied to multiple spark gaps was investigated.
2016,
28: 015019.
doi: 10.11884/HPLPB201628.015019
Abstract:
The effects of glow discharge frequency, current magnitude and treatment time are studied by using glow discharge to treat the insulator in order to improve the flashover voltage of insulator in vacuum. Experiment results show that the flashover voltage of insulator could be greatly improved through glow discharge pre-treatment. The flashover voltage of unconditioned insulator is 55 kV. After treating for 40 min by high frequency glow discharge, the saturated flashover voltage becomes 100 kV. After treating for 40 min by AC glow discharge, the flashover voltage reaches to 125 kV, which is 25 kV higher than that of high frequency glow discharge. Meanwhile，the larger the current is, the higher the saturated flashover voltage will be. However, as the current gets larger, the growth of flashover voltage saturates gradually.
The effects of glow discharge frequency, current magnitude and treatment time are studied by using glow discharge to treat the insulator in order to improve the flashover voltage of insulator in vacuum. Experiment results show that the flashover voltage of insulator could be greatly improved through glow discharge pre-treatment. The flashover voltage of unconditioned insulator is 55 kV. After treating for 40 min by high frequency glow discharge, the saturated flashover voltage becomes 100 kV. After treating for 40 min by AC glow discharge, the flashover voltage reaches to 125 kV, which is 25 kV higher than that of high frequency glow discharge. Meanwhile，the larger the current is, the higher the saturated flashover voltage will be. However, as the current gets larger, the growth of flashover voltage saturates gradually.
2016,
28: 015020.
doi: 10.11884/HPLPB201628.015020
Abstract:
A trigger circuit was developed for triggered vacuum switch (TVS) with more than 20 mm gap distance. The trigger circuit generate a high pulse voltage by pulse transformer, parallel a small capacitor on the output of the transformer and series a sharpening gap between the capacitor and the trigger surface. The output of trigger circuit is not affected by metal vapor deposition on trigger surface. Adjusting the gap breakdown voltage can increase charging voltage and energy storage of capacitor. Conduction tests for TVS were done with the trigger circuit. The results show that output energy of the trigger circuit was increased by adding the sharpening gap, regardless of the metal deposition on trigger surface. The trigger circuit can ensure 100% reliable conduction of TVS with a series sharpening gap between the capacitor and the trigger surface.
A trigger circuit was developed for triggered vacuum switch (TVS) with more than 20 mm gap distance. The trigger circuit generate a high pulse voltage by pulse transformer, parallel a small capacitor on the output of the transformer and series a sharpening gap between the capacitor and the trigger surface. The output of trigger circuit is not affected by metal vapor deposition on trigger surface. Adjusting the gap breakdown voltage can increase charging voltage and energy storage of capacitor. Conduction tests for TVS were done with the trigger circuit. The results show that output energy of the trigger circuit was increased by adding the sharpening gap, regardless of the metal deposition on trigger surface. The trigger circuit can ensure 100% reliable conduction of TVS with a series sharpening gap between the capacitor and the trigger surface.
2016,
28: 015021.
doi: 10.11884/HPLPB201628.015021
Abstract:
The time sequence control of the Marx generators, laser-triggered gas switches(LTS), self-break water switches (WS) which affects the PTS synchronization was studied. Synchronization of Marx generators affects energy efficiency of transmission process and PTS synchronization is mainly determined by LTS and SW. The key to achieve precise synchronization of the PTS is to independently and precisely adjust the trigger time of the 12 lasers, each laser is split into two beams used to trigger two laser triggered gas switches (LTGS). The LTGSs in the upper layer of PTS are triggered 20 ns later than the LTGSs in the lower layer to compensate the transmission time difference caused by length different between the transmission lines in the upper layer and the lower layer. The gap distances of the electrodes of the self-breaking water switches are set to suitable values to adjust the switching time. Experiments show that the synchronization jitters of the Marx generators, the main switches, the water switches, and the tri-plate transmission lines are 11, 4, 10 and 6 ns respectively. The 24 modules were well synchronized for the experimental shots. Currents of magnetically insulated transmission line (MITL) and load showed good repeatability with similar load.
The time sequence control of the Marx generators, laser-triggered gas switches(LTS), self-break water switches (WS) which affects the PTS synchronization was studied. Synchronization of Marx generators affects energy efficiency of transmission process and PTS synchronization is mainly determined by LTS and SW. The key to achieve precise synchronization of the PTS is to independently and precisely adjust the trigger time of the 12 lasers, each laser is split into two beams used to trigger two laser triggered gas switches (LTGS). The LTGSs in the upper layer of PTS are triggered 20 ns later than the LTGSs in the lower layer to compensate the transmission time difference caused by length different between the transmission lines in the upper layer and the lower layer. The gap distances of the electrodes of the self-breaking water switches are set to suitable values to adjust the switching time. Experiments show that the synchronization jitters of the Marx generators, the main switches, the water switches, and the tri-plate transmission lines are 11, 4, 10 and 6 ns respectively. The 24 modules were well synchronized for the experimental shots. Currents of magnetically insulated transmission line (MITL) and load showed good repeatability with similar load.
2016,
28: 015022.
doi: 10.11884/HPLPB201628.015022
Abstract:
The disk electrode of a gas switch with different materials is studied by self-breakdown experiment in slightly uneven electric field. In the self-breakdown experiment, the gap length and the gas pressure of the switches are identical .The gap length is 5 mm and the gas pressure is 0.25 MPa, so the self-breakdown voltage of each switch is almost 40 kV. Stainless steel, brass, tungsten-copper alloy and graphite are studied in the experiment. The differences of switch performance, like static performance, electrode mass loss and electrode surface, are compared in the research. The experiment result shows that the probability of self-breakdown at low working ratio of the graphite electrode switch is much lower than the others of metal material electrode switches. There is little difference of the static performances among the metal electrode switches. Mass loss of graphite electrode is higher than that of other electrodes. But, because most of the graphite ablation production is gas, the insulator of the graphite electrode switch is polluted much more lightly than that of others.The ablation of the tungsten-copper alloy electrode is lighter than that of others.
The disk electrode of a gas switch with different materials is studied by self-breakdown experiment in slightly uneven electric field. In the self-breakdown experiment, the gap length and the gas pressure of the switches are identical .The gap length is 5 mm and the gas pressure is 0.25 MPa, so the self-breakdown voltage of each switch is almost 40 kV. Stainless steel, brass, tungsten-copper alloy and graphite are studied in the experiment. The differences of switch performance, like static performance, electrode mass loss and electrode surface, are compared in the research. The experiment result shows that the probability of self-breakdown at low working ratio of the graphite electrode switch is much lower than the others of metal material electrode switches. There is little difference of the static performances among the metal electrode switches. Mass loss of graphite electrode is higher than that of other electrodes. But, because most of the graphite ablation production is gas, the insulator of the graphite electrode switch is polluted much more lightly than that of others.The ablation of the tungsten-copper alloy electrode is lighter than that of others.
2016,
28: 015023.
doi: 10.11884/HPLPB201628.015023
Abstract:
In this paper, a microsecond-pulse generator with a rise time of about 0.5 s, a pulse width of about 6 s and an amplitude of up to 40 kV, and a nanosecond-pulse generator with a rise time of about 150 ns, a pulse width of about 300 ns and an amplitude of 50 kV, were used to produce diffuse discharges at atmospheric pressure. A saw-blade and a knife blade were used as the electrodes. Characteristics of diffuse discharges under different conditions, in different cases of the applied voltage, pulse repetition frequency (PRF), anode structure and gap distances, were investigated by analyzing the voltage-current waveforms and discharge images. The experimental results showed that both microsecond-pulse and nanosecond-pulse power supplies could generate large-area diffuse discharges, and the maximum area reached 90 cm2. The uniformity of diffuse discharges were significantly affected by the pulse parameters and anode structure. The best homogeneity could be obtained in the case of a knife blade when nanosecond-pulse generator was used. Furthermore, under the same conditions, the instantaneous power for nanosecond-pulse discharges was larger than that for microsecond pulse discharges, and the largest instantaneous power was 275 kW. However, the energy for nanosecond-pulse discharges was smaller than that for microsecond pulse discharges. In addition, other things being equal, the conduction current decreased with the increase of the gap distance, the discharge intensity increased with the PRF, and the working range of the applied voltage significantly decreased with the PRF. Therefore, its most likely to obtain homogeneous diffuse discharges with wide range of working voltages in atmospheric pressure air when the knife blade electrode was used as the anode at low PRF.
In this paper, a microsecond-pulse generator with a rise time of about 0.5 s, a pulse width of about 6 s and an amplitude of up to 40 kV, and a nanosecond-pulse generator with a rise time of about 150 ns, a pulse width of about 300 ns and an amplitude of 50 kV, were used to produce diffuse discharges at atmospheric pressure. A saw-blade and a knife blade were used as the electrodes. Characteristics of diffuse discharges under different conditions, in different cases of the applied voltage, pulse repetition frequency (PRF), anode structure and gap distances, were investigated by analyzing the voltage-current waveforms and discharge images. The experimental results showed that both microsecond-pulse and nanosecond-pulse power supplies could generate large-area diffuse discharges, and the maximum area reached 90 cm2. The uniformity of diffuse discharges were significantly affected by the pulse parameters and anode structure. The best homogeneity could be obtained in the case of a knife blade when nanosecond-pulse generator was used. Furthermore, under the same conditions, the instantaneous power for nanosecond-pulse discharges was larger than that for microsecond pulse discharges, and the largest instantaneous power was 275 kW. However, the energy for nanosecond-pulse discharges was smaller than that for microsecond pulse discharges. In addition, other things being equal, the conduction current decreased with the increase of the gap distance, the discharge intensity increased with the PRF, and the working range of the applied voltage significantly decreased with the PRF. Therefore, its most likely to obtain homogeneous diffuse discharges with wide range of working voltages in atmospheric pressure air when the knife blade electrode was used as the anode at low PRF.
2016,
28: 015024.
doi: 10.11884/HPLPB201628.015024
Abstract:
Except for the integrated charge transferred, the effective area of discharge electrode and pollution of discharge spatters on insulator shell are major limiting factors to the gas spark switch lifetime. After theoretic analysis, increasing electrode area with uniform discharge can improve switch lifetime effectively. We have designed a new three-coaxial-electrodes structure, whose electric field simulation results show nice uniformity in both charging state and triggering state. Meanwhile, a circulative gas path can control the splash direction of discharge spatters to reduce the pollution of insulators inner wall, and enhance the gas insulation recoverability to prolong switchs lifetime. We have carried out the experiments under the repetitive condition (40 kV/20 kA/0.1 Hz). Result shows that this long-lifetime gas spark switch works stably, whose self-breakdown voltage characteristic and trigger delay jitter characteristic are both as good as expected, and single switch has worked more than 13.7105 shots.
Except for the integrated charge transferred, the effective area of discharge electrode and pollution of discharge spatters on insulator shell are major limiting factors to the gas spark switch lifetime. After theoretic analysis, increasing electrode area with uniform discharge can improve switch lifetime effectively. We have designed a new three-coaxial-electrodes structure, whose electric field simulation results show nice uniformity in both charging state and triggering state. Meanwhile, a circulative gas path can control the splash direction of discharge spatters to reduce the pollution of insulators inner wall, and enhance the gas insulation recoverability to prolong switchs lifetime. We have carried out the experiments under the repetitive condition (40 kV/20 kA/0.1 Hz). Result shows that this long-lifetime gas spark switch works stably, whose self-breakdown voltage characteristic and trigger delay jitter characteristic are both as good as expected, and single switch has worked more than 13.7105 shots.
2016,
28: 015025.
doi: 10.11884/HPLPB201628.015025
Abstract:
Operating principle of series diode is introduced and an equivalent circuit of series diode is built to analyze its working process. Circuit simulation is done to find the influencing factors of series diode working process. Voltage dividing of series diode includes four phases: first, voltages of each diode are divided according to capacitances of each diode. Second, voltages of each diode are divided according to the first diode impendence and second gap capacitance. Third, Voltage dividing enters into a dynamic balancing phase relating to all the parameters after both cathodes emitting electrons. Finally, Voltage dividing is determined by the impendence of each diode. Capacitances and vacuum breakdown voltages of diodes are the major influencing factors of voltage dividing in the primary stage, and impedance variation and vacuum breakdown time of each gap have important impact on voltage dividing in the dynamic balancing phase.
Operating principle of series diode is introduced and an equivalent circuit of series diode is built to analyze its working process. Circuit simulation is done to find the influencing factors of series diode working process. Voltage dividing of series diode includes four phases: first, voltages of each diode are divided according to capacitances of each diode. Second, voltages of each diode are divided according to the first diode impendence and second gap capacitance. Third, Voltage dividing enters into a dynamic balancing phase relating to all the parameters after both cathodes emitting electrons. Finally, Voltage dividing is determined by the impendence of each diode. Capacitances and vacuum breakdown voltages of diodes are the major influencing factors of voltage dividing in the primary stage, and impedance variation and vacuum breakdown time of each gap have important impact on voltage dividing in the dynamic balancing phase.
2016,
28: 015026.
doi: 10.11884/HPLPB201628.015026
Abstract:
The frequency response of B-dot monitors fielded in the cavity of magnetically-insulated transmission lines is analyzed. The equivalent sensitivity of B-dot monitors in the cavity could be increased at low frequencies. The B-dot monitor behaves approximately as if its signal were transmitted though a high-pass RC filter with negative RC time constant, and the lower frequency components are amplified. The experiments were carried on at different equivalent frequencies. It shows that both the characteristic flux-penetration time and the mutual inductance between the main circuit and the B-dot monitor are different while the frequency of the test signal is changed. The equivalent bandwidth of calibration waveform should approach the real waveform to get the exact correcting coefficients.
The frequency response of B-dot monitors fielded in the cavity of magnetically-insulated transmission lines is analyzed. The equivalent sensitivity of B-dot monitors in the cavity could be increased at low frequencies. The B-dot monitor behaves approximately as if its signal were transmitted though a high-pass RC filter with negative RC time constant, and the lower frequency components are amplified. The experiments were carried on at different equivalent frequencies. It shows that both the characteristic flux-penetration time and the mutual inductance between the main circuit and the B-dot monitor are different while the frequency of the test signal is changed. The equivalent bandwidth of calibration waveform should approach the real waveform to get the exact correcting coefficients.
2016,
28: 015027.
doi: 10.11884/HPLPB201628.015027
Abstract:
We have measured X-ray, optical and microwave radiations from two parallel wires driven by a current rising to 220 kA in 100 ns. The experimental results imply that they are generated by different radiation mechanism. X-ray is generated by thermal radiation which is proportional to ohmic heating of wires. Optical radiation is from thermal emission and line emission, but microwave radiation is produced by non-thermal radiation. The dependence of radiation on distance between two wires demonstrates that increasing the coupling between two wires can enhance non-thermal radiation, but is detrimental to thermal radiation. For driving condition of 100 kA per wire used in our experiments, the critical distance where the two wires decouple is approximately 10 mm. It appears that the coupling between wires plays a fundamental role in electromagnetic radiation produced by Z-pinch.
We have measured X-ray, optical and microwave radiations from two parallel wires driven by a current rising to 220 kA in 100 ns. The experimental results imply that they are generated by different radiation mechanism. X-ray is generated by thermal radiation which is proportional to ohmic heating of wires. Optical radiation is from thermal emission and line emission, but microwave radiation is produced by non-thermal radiation. The dependence of radiation on distance between two wires demonstrates that increasing the coupling between two wires can enhance non-thermal radiation, but is detrimental to thermal radiation. For driving condition of 100 kA per wire used in our experiments, the critical distance where the two wires decouple is approximately 10 mm. It appears that the coupling between wires plays a fundamental role in electromagnetic radiation produced by Z-pinch.
2016,
28: 015101.
doi: 10.11884/HPLPB201628.015101
Abstract:
In the commissioning of a linear induction accelerator, cavity voltage waveforms measured by capacitor voltage probe (CVP) and resistor divider were almost the same when there was no beam load. The waveforms were different when there was a beam load. This phenomenon was then researched. Cavity voltage waveforms were simulated when the beam was advanced, synchronized and delayed. Simulation results showed that time difference caused by cavity structure was the main reason for the waveform differences. The distribution parameter circuit model of the accelerating cavity was created. It was shown that the beam load arrived at the two probes by different moments, which would lead to the difference of the cavity waveforms. The waveform measured by CVP was closer to the real accelerating waveform because that the CVP was nearer to the accelerating gap. The measured beam load waveforms verified that the beam load arriving times of two probes were different. The measured energy spectrum of accelerated beam was also consistent with the addition of CVP waveforms. As a result, the simulation and analysis methods in this research were effective. They would be used in commissioning and performance optimization of the accelerator.
In the commissioning of a linear induction accelerator, cavity voltage waveforms measured by capacitor voltage probe (CVP) and resistor divider were almost the same when there was no beam load. The waveforms were different when there was a beam load. This phenomenon was then researched. Cavity voltage waveforms were simulated when the beam was advanced, synchronized and delayed. Simulation results showed that time difference caused by cavity structure was the main reason for the waveform differences. The distribution parameter circuit model of the accelerating cavity was created. It was shown that the beam load arrived at the two probes by different moments, which would lead to the difference of the cavity waveforms. The waveform measured by CVP was closer to the real accelerating waveform because that the CVP was nearer to the accelerating gap. The measured beam load waveforms verified that the beam load arriving times of two probes were different. The measured energy spectrum of accelerated beam was also consistent with the addition of CVP waveforms. As a result, the simulation and analysis methods in this research were effective. They would be used in commissioning and performance optimization of the accelerator.
2016,
28: 015102.
doi: 10.11884/HPLPB201628.015102
Abstract:
A new method with frequency domain processing was used in processing the output signals of axial B-dot beam angle monitor. By this method, the valuable signals were derived from the signals in frequency domain with other disturbing signals eliminated and with a certain amount that were related with beam position. This method is a good complement to that with time domain processing and more suitable for modeling of actual complex axial B-dot circuit, but the measurement errors caused by the alignment error could not be reduced while the displacements of beam are large. The measurement error of frequency domain processing was approximate to that of time domain processing with value of 1 mrad according to the measurement using a test stand.
A new method with frequency domain processing was used in processing the output signals of axial B-dot beam angle monitor. By this method, the valuable signals were derived from the signals in frequency domain with other disturbing signals eliminated and with a certain amount that were related with beam position. This method is a good complement to that with time domain processing and more suitable for modeling of actual complex axial B-dot circuit, but the measurement errors caused by the alignment error could not be reduced while the displacements of beam are large. The measurement error of frequency domain processing was approximate to that of time domain processing with value of 1 mrad according to the measurement using a test stand.
2016,
28: 015103.
doi: 10.11884/HPLPB201628.015103
Abstract:
For the requirements of SGEMP research, the Flash-Ⅱ accelerator has been transformed to improve the simulation capability of pulsed hard X rays. A two-stage waterline together with its water switches was adopted to upgrade the driver. The experimental results show that the designed performance has been achieved. With a much shorter risetime of 30 ns, the transformed accelerator now can reliably output a 60 ns width voltage from 650 kV to 1.3 MV. Using the accelerator, a diode with two stages in series has been developed and 53 ns pulse X-rays with risetime of 29 ns have been obtained successfully.
For the requirements of SGEMP research, the Flash-Ⅱ accelerator has been transformed to improve the simulation capability of pulsed hard X rays. A two-stage waterline together with its water switches was adopted to upgrade the driver. The experimental results show that the designed performance has been achieved. With a much shorter risetime of 30 ns, the transformed accelerator now can reliably output a 60 ns width voltage from 650 kV to 1.3 MV. Using the accelerator, a diode with two stages in series has been developed and 53 ns pulse X-rays with risetime of 29 ns have been obtained successfully.
2016,
28: 015104.
doi: 10.11884/HPLPB201628.015104
Abstract:
Circuit models and mathematical expressions are built to analyse how much the circuit parameters of induction cavity affect the flattop of the induction pulse voltage. Two kinds of pulse-power system (PPS) are considered, one is based on the pulse forming lines (PFL) and pulse transmission lines, and the other is based on the capacitors and solid state switches. Much difference appears when the cavity works with different PPS. Using the comparison expressions including capacitance, inductance and resistance of the induction cavity and corresponding PPS, we can determine the circuit parameters of a pulse induction module exactly and easily.
Circuit models and mathematical expressions are built to analyse how much the circuit parameters of induction cavity affect the flattop of the induction pulse voltage. Two kinds of pulse-power system (PPS) are considered, one is based on the pulse forming lines (PFL) and pulse transmission lines, and the other is based on the capacitors and solid state switches. Much difference appears when the cavity works with different PPS. Using the comparison expressions including capacitance, inductance and resistance of the induction cavity and corresponding PPS, we can determine the circuit parameters of a pulse induction module exactly and easily.
